Problem: Nadia is 4 times as old as Tiffany and is also 15 years older than Tiffany. How old is Tiffany?
Explanation: We can use the given information to write down two equations that describe the ages of Nadia and Tiffany. Let Nadia's current age be $n$ and Tiffany's current age be $t$ $n = 4t$ $n = t + 15$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $t$ , and both of our equations have $n$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $4t$ $-$ $ (t + 15)$ which combines the information about $t$ from both of our original equations. Solving for $t$ , we get: $3 t = 15$ $t = 5$.